Journal of Scienti fic & Indust ri al Research

VoL 62 , Jul y 2003, pp 707 -7 13

Generation of Chlorinated Organic Material in Eucalyptus Pulp Bleaching Using Different Bleaching Sequences

M Roy*, S K Chakrabarti , N K Bharadwaj , Sandip Chandra, Sanjay Kumar Sarabj eet Singh and P K Bajpai

T hapar Cent re fo r Industri al Research & Development , Bhadson Road , Pati a la 147004

and

M B l auhari

T-57 , Sector 12 , Noida 20 I 30 I

Received: 17 October 2002; accepted : 17 January 2003

Eucalyptus is onc of the important pul ping raw mate ri a ls in India, Australia , Braz il , South East Asi an and European countries , and South Afri ca. Kraft pul ping and bleaching wi th chl orine, hypochl orite and chl orine d ioxide is co nside red to generate e fflu ent s containing tox ic o rganochlorines. Thi s study deals with the kraft pulping o f eucalyptu s and convent ional bleaching with chlo rine, hypochl ori te and chl o rine dioxide and characteri zation of e ftluents fo r tox ic po llutants. Effect of di ffe rent pu lp ing and bleaching condi ti ons on the generati on of pollutant s, e.g. , colour, COD, AOX , EO X, EOX , PO X is also studied.

Keywords : Eucalyptu s pul p, Bleaching, Chl orinated o rgani c mate ri al, Kraft pulping

Introduction

During chl orine bleaching of pulp, about 10 per cent of the chlorine used gets bound to the res idual li gnin and forms chl orinated organics . The rest of the chlorine (about 90 per cent) end s up as common salt. Chl orinati on of pulp results in an increase in free phenolic hydroxyl groups and carboxy l groups and a dec rease in the molecul ar we ight of li gnin , which makes the lignin eas il y solubl e in water and alkaline so lution. Vari ous kinds o f chl orinated pheno ls, pheno lic carboxy li c ac ids, dicarboxy lic ac ids, res in ac ids and hydrocarbons orig inating from li gnin and/or extracti ons of wood are found to be present in the bl each efflu ent 1- 12 . These chlorinated organics are termed as AOX (adsorbable organi c ha logen). The fracti on ( 1-3 per cel}t) of adsorbable organic halogen, which is ex trac table by a non-polar organic sol vent , is refe rred to as EOX (ex trac table organi c hal ogen). Thi s fracti on contains re lati ve ly lipophilic (fat so lubl e) neutra l organic compounds, primaril y of low molecular we ight and IS therefore of greate r environmental signifi cance compared with the

* Author for correspondence: Fax: +9 1- 175-23640 12; E- mail: roy @th aparresearch.org

remaJl1J11g AOX. There is another part of organochlorine compound , which is highl y vo lat ile and is known as POX (purgeabl e organi c halogen). The components of particular concern in the polychlorinated aromatic materi a l that have re lati ve ly hi gh level of chlorine substituti on (3-4 c l atoms per aromatic ring) are known as polychl orinated dibenzo­p-dioxins (PCDD) and furans (PCDF) 11 14. Some of these compounds a re of tox icological concern. However the maj or toxic compounds in thi s catego ry are tetrachloro dioxin (TCDD) and te trachl oro di furan (TCDF). The detecti on of TCDDs and TC DFs in pulp and paper mill effluents prompted many researc hers to study the re lease and control o f toxic pollutants in the pulp bleaching process with c hl orine or chl orine derivatives .

Soft woods which are used in la rge proporti on by European and North American countri es for pulping processes, are reported to re lease hi gher amount o f chlorinated organics (5- 10 kg AOX/t pulp) on chlorine bleaching as compared to hardwood pul ps (3-5 kg AOX/t pulp) 15 for controlling the re lease of chlorinated organic pollutants, Scandinav ian and other European countries are spearheading for the tota ll y chlorine-free bleac hing (TCF) process,

708 J SCI IND RES VOL 62 JULY 2003

whereas the North American countries (Canada and the US) and Japan are sati sfi ed with e lementa l c hl orine-free bleaching (ECF) process, where in chl orine compounds like chlorine diox ide are still

be i ng used .

Eucalyptu s is one o f the important pulping raw mate ri a ls in Ind ian subcontinent and severa l other countries including Austra lia , Brazil and European community. In Indi a, pulps hav ing hi gh bri ghtness a re made by kraft pulping, fo llowed by conventional bleaching, us ing chl orine and c hlorine based chemica ls. Bleac hing with chlorine che micals is considered to produce tox ic organochlorine compounds. However, the re is not much systematic informati on ava ilable on the generation of toxic po llutants. A hybrid euca lyptus varie ty (Eucalyptus tereleco l"lli s) is used in the present study for kraft pulping, bleaching and characterizat ion o f bleac h effluents for the ir po llutant s.

Experimental Procedure

A. Pulping

The pulping of euca lyptus chips was done in a Lab Autoclave Di geste r (U niversa l, 1ndia make). The digested wood chips were di spersed in a pulp di sintegrator and the pulp was washed to remove the bl ack liqu or and di ssolved substances in the washing centrifuge (Chemo' Fab make, 1440 rpm). The moisture content and kappa nu mber of the unbl eac hed pulp were determined subsequentl y. The deta ils of the pUlping conditions are given in T able I .

B. Bleaching

Prior to bleaching, disintegration of the unbleached pulp was carri ed out at 3 pe r cent

consistency for 4-5 min us ing a pu lp di sintegrator. The dispersed pulp thus produced, was filtered, washed, and collected for subseque nt bleac hing studies. For chlorination of pulp, adequate quantity of ch lorine water and tap water were added to the pulp s lurry in a plastic container and the mi xture was shaken inte rmittently (at an inte rva l of 10 min) for 45 min . Afte r the reac tion was over, pulp slurry was filtered and the filtrate was co llected in a previous ly cooled fla sk. The pulp was was hed with 500 mL of water in two stages and the filtrate in each stage was passed th rough the pulp mat so that res id ua l fines get entrapped in pulp mat. The bleaching conditions fo r di ffe rent sequences a re g iven in Tabl e 2 . The filtrate and washings were co ll ec ted, mi xed and stored in a refri ge rator for characte rization .

For C I02 (0 stage) bleaching the pu lp s lurry was taken in a pol ythene bag, CI02 water was added which was prepared by adding HC I to <.lC I0 1 and the strength of CI02 was dete rmined as per Tappi method (T6 11 om- 84) and was shaken inte rmi tten tl y at 70°C for 3 h.

In Eo stage the pulp was taken ill a po lythenc beaker, adequate qu antity of water LInd sodium hydroxide soluti on were added. The pulp s lurry was mi xed manua ll y with a spatu la. It was then tran sferred to the bombs of Autoc lave digeste r. T he pulp s lurry was kept under oxygen pressure and a te mperature of 60 DC was mainta ined. After 2 h, oxygen pressure was re leased and the pulp was fi lte red under vacuum. It was subsequently washed with water tw ice. The filtrate and the washings ( in each stage) were once more rec irculated. Fina ll y the entire filtrate and washings were co llected, mixed , and stored for characterization .

Tab le 1- Pulping of eucalyptus

Particu lar

Acti ve alkal i as per cent Na20 , (on 0 d chips)

SulphidilY of white liquor, per ceIll

Bath rati o

Cooki ng cycle

Kappa number of pulp·

For bleaching sequence*

2 3

19.0 17.0 2S.0

12.5 25.2 25 .2

1:3.5 1:3.5 1:3

60 min to 130 "C 90 min to 165 "C 60 min to 130"C

30 min at 130 "c 90 min at 165 "c 30 min at 130 "c

4

n.o ~5.2

1:3

30 min 10 130 "C

30 min <1t 130 "C

60 min to 165 "C

75 min at 163"C

60 min to 165 "C 60 min from 130- 161 "C

75min atl 63"C 45minatl 6 1"C

22.5 20.2 19.7 I S.7

ROY el (I I.: GENERATIO ' OF CHLORINATED ORGANIC MATERIAL IN EUCALYPTUS PULP BLEAC HI NG 709

Parti cul ar

C stage

CI2 added, per cent

CI2 consumed, per cent

Final pH

H, s/{{ge

Cl 2 added. per cent

NaO H added. per cenl

Cl 2 conslIJlIed. per cenl

Inilial /Final pH

Brigthness , per cent ISO

H ] slage

CI 2 added, per celll

N:10 H added , per celll

CI2 co nsumed, per celll

Initia l/Final pH

Brigtil ness. per cent ISO

C/J slage

CI 2 added , per cenl

Cl l consumed . per cenl

Cl02 added , per cent

CI2 consumed, per cent

Final pH

Eo slage

aOH added , per cent

O2 pressure, kg/cm2

Initia l/Fin al pH

Brighlness, per cenl ISO

f) I slage

CI02 added . per cen l

CIO] consumed, per cen l

In it ial fin al pH

Brightness, per cent ISO

O2 swge

Cl02 added , per cent

CIO] co nsumed , per cen t

Tab le 2 - Bleaching of eucalyptus pu lp

For bleaching sequence*

5.20

5.05-5. 14

IA- 2.0

3AO

1.5-1.9

3.39

10.6- II A/6.9-7.6

72. 1· 72.2

11 5

0.22-0.25

OA2-0A5

10.7-10.9/8.0-8.2

8 1.0-8 I A

2

2.2

2. 19

0.84

0.83 -0.84

I. 9-2. I

1.4-2.2

5.5

11.7- 12.6/ 10.8- 11.5

5 1.0-53 .3

0.76

0.75

2.8-2.9/2.8-2 .9

80.9-8 11

0.38

0.32-0.37

3

4.55

4.52-4.53

1.7-1 .1)

3.50

0.7

1.95-2.02

11.7-11 .8/7.7-7. 8

82.5-82.6

0.60

0. 12

OA7-0A8

8.9-9 . 117.5-7.7

85. 3-87.1

4

2.25

OA5

1.7.''' -1 . '()

11 .2- 11.3/7.:'-7.7

84.8-8"- .1)

0.25

0.02

0 . 16-0. 18

8A-8.5/7A-7 .5

86.6-88.3

U-·U

3.77-4.37

0 . 16-0.18

0. 11 -0. 15

2. 1

1.8- 2.0

1.5

I 1.5-1 2.6/9.6- 1 1.0

48.9-50.5

- COnld

7 10 J SCIINO RES VOL 62 JULY 2003

Table 2 - Bleaching of eucalyptus pulp - (Coll/e!)

Part icu lar

Initi al/ li nal pH

Brightncss. per cent ISO

£" SlagI'

NaO H added , per cent

H20 2 added, per cent

H20 2 consumed, per cent

Initia l/Fin al pH

Brightncss per cen t, ISO

For hypo stages (H, and H2) the pulp was taken In a polythene bag, pH was maintained at - 10 by sodium hydrox ide, 0.1 per cent sulphamic acid was added , followed by calc ium hypochl orite the doses was dec ided depending upon the kappa no. of the pulp obtained from the previous bleaching step. It was shake n intermittentl y at 40°C for 3 h.

The pulp consistency was 3 per cent in chl orinati on stage, 4 per cent in Co stage and 10 per cent in a ll other stages. The treatment temperature was 30 "c for C stage, 40-45 "c for CD stages , 65 DC fo r Eo and Ep stages , 40°C for H" 35 °C for H2 and 75 "c fo r 0 , and O2 stages. The treatment t ime was 45 min for C and CD stages , 120 min for Eo and Ep stages , 180 min for H " 120 min for H2, and 180 min for 0 stages. All the bleaching experiments were conducted with 100- 134 g pulp and repeated at leas t four times.

The filtrate and subsequent washings in each stage o f bleac hing of the pulp were immediate ly co llected and measured . The comb ined filtrate and wash ings for ana lys is were fill ed to the brim in a 250 mL polythene bottle and kept be low 4 °C. POX analysis o f the samp les was completed within 7 d and other tests for conventi onal and non-conventional pollutants were compl eted within 30 d.

C. Analysis

Kappa no. of pulp, available chl ori ne in chl orine wate r and c hl orine di ox ide were dete rmined as pvr Tappi Standards.

Brightness of the pulp was dete rmined ll si ng Tec hnibrite Brightness Meter (Mode l TB-I C).

For bleaching sequence*

2

2.8/2.8-3.0

85.0-85 .8

3

2.5

0.5

0.49

11.8- 12. 1/ 10.2- 10.5

42.3-43.5

4

Colour, COO and BOD were de termined fo llowing the methods as pe r 'S tandard Meth ods for the Examination of Water and Wastewater' (APHA), 181h

edition, 1992. AOX, EOX, and POX were de term ined with ECS 2000 AOX analyzer (Euroglas BY, The Netherlands) as follows:

AOX was de te rmined as pe r ISO Method no. 9562: 1989 (E) using AOX cassette . The method involves the following steps : acidifi cation of wate r sample with HNO" treatment with Na2SO, to remove active Cb, adsorption on activated charcoal of the organochlorines, removal of inorgani c halogen by rinsing with NaNO, so lution, combust ion of the loaded charcoal in an oxygen stream, dete rminati on of hydrogen chloride by microcou lometry.

EOX was de te rmined as pe r th e procedure outlined in In strument Manual us ing EOX cassette with the same AOX Analyzer. Following steps were fo ll owed : Treatment with Na2S0, to remove act ive C12, extraction of the sample with Il-hexane, drying of so lvent-extract over anhydrou s Na2SO.j, d ist illati on of so lvent-ex tract to reduce the vo lume to 5-10 mL, addition of 10 per cent hexadecane to the so lvent ­ex tract, injection of the sample, combust ion, fo ll owed by microcoul ometri c determinati on o f hydrogen chl oride.

POX was also dete rmined as pe r the procedure outlined in Instrument Manual using POX cassette with the AOX anal yzer. In thi s analysi s, appropri ate dilution of the sampl e was made using de ioni zed water, followed by purging with oxygen, co mbu sti on, and microcoulometric dete rminat ion of hydrogen chloride .

ROY et al.: GE ERATION OF CHLORINATED ORGANIC MATERIAL IN EUCALYPTUS PULP BLEACHI NG 711

Results and Discussion Generation of po llutants during eucalyptus pu lp

bleaching in four different sets of pulping and bleaching conditions are reported in Tables 3-6. From these data, it has been observed that the pu lping and bleaching conditions have a great effect on the generation of pollutants during eucalyptus pulp production.

The targeted kappa nos. of these unbleached pu lp and brightness of the fina l pu lp were - 20 and 86-88 per cent ISO, respective ly, in CI)EoH JH2 bleaching sequence (Table I ). The tota l colour load of the effluent was 95.7 kg/t and most of it was generated in the CD and Eo stages onl y (Table 3) , whereas the colour load from the bleaching of bamboo by simi lar pulping and bleaching process has

Table 3 - Generation of po ll utants in eucalyptus pu lp bleaching using CoEoH I H2 sequence

Stage Co lour (kg/t pu lp) COD (kg/t pulp) AOX (kg/t pulp) EOX (g/t pulp ) POX (g/ t pulp)

CD 3332.0. 10) 18. 73 (2.20) 2. 14 (0.24) 51.04 (22.0) 18. 52 (2.40)

Eo 6 1.90 (9.50) 3 1.90 ( 1.60) 0.52 (0.04) 29.75 (5.25) 0.46 (0.04 )

HI 0.37 (0.08) 4.94 (0.46) 0.40 (0.05) 59.80 (10.90) 40.61 ( 1.0 1)

H2 0.07 (0 02) 0.94 (0. 14) 0.05 (0.03) 42 .97 (9.03) 5.80 ( 1.00)

Total 95.66 56.5 1 3. 11 183.56 65.39

Va lues in parenthesis are stalldard deviat ions

Table 4 - Generati on of pollutants in eucalyp tus pulp bleaching usi ng CoEoDID2 sequence

Stage Co lour (kg/t pu lp) COD (kg/t pulp) AOX (kg/t pulp) EOX (g/t pulp) POX (g/t pulp)

Cu 51.20 (4.80) /6.12 (0.72) 1.1 3 (0.04) 16.03 (3.70) 1.2 1 (0.02)

Eo 4930 ( 1.60) 26.34 (3.60) 0.26 (0.05 ) 17.59 (4.22) Not detected

DI 2.10(0.49) 2.22 (0.34) 0.06 (001 ) 11.30 (370) 0.74(0.54)

D 2 0.58 (0.12) 0.90 (0.07) 0.02 (0.01 ) 19.7 1 (0.63) 2 1.9 1( 15.00)

Total /03. 18 45.58 1.47 64.63 2H6

Va lues in parenthesis are standard deviations

Table 5 - Generati on of pollutants in eucalyptus pu lp bleaching using CH IH2 sequence

Stage Colour (kg/t pulp) COD (kg/t pulp) AOX (kglt pulp) EOX (g/t pulp) POX (kg/t pulp)

C 53 .70 (8.90) 24.90 (1.0 I) 201 (0.25) 76.50 (8.60) 2 1. 99(2.00)

HI 9.00 (1.04) 13.90 (0.34) 1.93 (0. 14) 10.23 (2 .44) 68.18( 19.40)

H2 0.11 (0.01) 2.60 (0.07) 0.24 (0.08) 27 .35 ( I 1.00) 15 .60(3.96)

Total 62.81 41.40 4.18 11 4.08 105.77

Valucs in parenthesis are standard deviations

Table 6 - Generation of pollutants in eucalyptus pulp bleaching using CEpHIH2 sequence

Stage Colour (kglt pulp) COD (kglt pulp) AOX (kglt pulp) EOX (glt pulp) POX (glt pulp)

C 7000( 16.00) 18.10(0.54) 1.98(0. 14) 96.30( 12.00) I 0.90( 1(0)

Ep 109.50(920) 30.25(6.90) 0.85(0.05) 14.82(2.30) 0.6 1 (0. 13)

HI 0.24(0.13) 3.09(0.28) 0.34(0.03) 93.23(25 .60) 54.60(9.00)

H2 0.33(0.06) 2. 11 (0.65 ) 0.13(0.02) 65.50(5.20) 23.95(2.20)

Total 180.07 53.55 3.30 269.85 90.06

Values in parenthesis are standard deviat ions

712 J SCIIND RES VOL 62 JULY 2003

been reported to be relatively higher 149 kg1t 16. This

indie Jtes that the poll utant generati on also depends on the raw material. The total COD load of the entire bl eac hing process was 56.5 kg/t of pulp, of which about 90 per ce nt was generated in CD and Eo stages. Thi s va lu e is quite c lose to the one reported for bamboo pulp bleaching under similar conditi ons. The AOX. EO X, and POX were 3. I kg/t, 183.6 g/t and 65.4 g/t, respecti vely (Tab le 3), whi ch were relat ively lower as compared to those fronl bamboo l 6

.

AOX generat ion was - 7 per cent of the totai chl orine consumed as compared to - 10 per cent, ge nera ll y obta in ed with softwood pulp 17. EOX val ue was 6 per cent of AOX . POX generation was maximulll in the HI stage. It may be attri buted to the fact that chl orine substituti on occurs in the degraded li gnin products resu lting in low molecular weight compounds.

In CDEo DI D2 sequence of bleaching the targeted kappa no. of unbleac hed pu lp and final brightness of bleached pulp were - 20 and 85-86 per cent ISO, respec ti ve ly. Overall co lour load in the effluent was 1m kg/t (Tab le 4). The total AOX generation was less than 1.5 kg/t, 76 per cent of which was generated in CD stage al one. Howeve r the COD load of - 46 kg/t was lo\ver as compared to that in CDEoH,H2 sequence. The EOX of 65 g/t and POX of 24 glt were also quite low in this sequence of bleaching due to use of chl orine dioxide in pl ace of hypo in the las t two stages and greater substi tuti on of chl orine with chl orine di oxide at CD stage . Generally the generation of organochl ori nes is lower in CIO] bleaching as

d I . II . bl I' IS I') TI' compare to t lat In C 1 onne eac llllg ' . li S may be due to the format ion of HOCI which generates less chl orinated organi cs .

In CH i fh bleaching sequence (mostly fo ll owed in small pulp mills using agro res idues) the targeted kappa no. and final bleached brightness were 22-23 and 8 1-82 per cent ISO, respecti vely. The colour and COD generati ons were 63 and 4 1 kg/t, respecti vely (Tah le 5) whi ch were quite low as compared to those in other bleac hing sequences in spite of hi gher li gn in content in the pulp . T hi s may be due to the fact that hypochl orite modifies the li gnin structure without des troy in g the chromophoric groups. The AOX ge nerati on is higher (4 .18 kg/t) , as expected, because of hi gher P. no. EOX is generated mostl y at C stage, th ough total POX generation is higher in HI and H2 stages compared to C stage (Table 5).

In CEpH IH2 bleaching sequences, the brightness of pulp is 84-86 per cent ISO. Generati on of co louring substances is quite hi gh ( 180 kg/t) compa red to CnEoH I H2 sequence (Tab le 3). Hydrogen peroxide reinforced alka line extracti on (Ep) IS mainl y responsible for hi gh colour load . However. the COD load IS comparable to CnEoH I H" sequence. Generat ion of organochl orines (AOX, EOX. POX) is higher (Tab le 6) compared to that observed with CDEOHIH2 sequence. EOX generation is quite high in all four stages of bleaching which coul d be probabl y due to higher kappa no. (22.5 against 19-20 in other cases) of the unbleached pulp, whi ch requ ires hi gher doses of chl orine, resultin g in the generation of hi ghl y ch lorinated aromatic co mpounds.

Conclusions

The study indicates th at pul ping and bleaching conditi ons have a great impact on generati on of poll utants in the bleaching effluent. Hypochlorite bl eaching of eucalyptus generates apprec iab ly lower amount of co lour in the bleach effl uent. CIO} bleaching significantl y reduces the generati on of organochl orine pollutants (AOX, EOX and POX).

AOX generati on from eucalyptu s pulp bleaching wi th different conditi ons vari es from 4.7-5.8 per ce nt of chl orine consumpti on and EOX is 1.73 to 8.1 8 per cent of AOX . Substitution of chlorine with CI02 in chl orinati on and subsequent stages significantl y reduces the AOX and EOX generati on. The former is onl y about 2 .0 per cent of combined consumpti on of CI2 and CI02 and EOX is onl y 4.4 per cent of AOX.

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